Background: Over 45% of American women 20–39 years old are at risk for type 2 diabetes, cardiovascular disease, and other health conditions because they are overweight or obese. The prevalence of overweight and obesity is disproportionately high among low-income women. This paper describes the study design and rationale of a community based intervention (Mothers In Motion, MIM) aimed to prevent weight gain among low-income overweight and obese mothers18-39 years old by promoting stress management, healthy eating, and physical activity. Methods/Design: Peer recruiters approach participants from 5 Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) in Michigan. The MIM delivers theory-based, culturally-sensitive intervention messages via a combination of DVDs and peer support group teleconferences (PSGTs). The DVD features African American and white overweight and obese WIC mothers who participated in a healthy lifestyle intervention patterned after MIM. The PSGTs are led by paraprofessionals from Michigan State University Extension and WIC providers in Michigan who are trained in motivational interviewing and group facilitation skills. Participants are randomly assigned to an intervention (n = 350) or comparison group (n = 175). The intervention group receives a 16-week intervention on a weekly or bi-weekly basis. Participants are asked to watch 10 MIM DVD chapters at home and join 10 PSGT sessions by phone. The comparison group receives printed educational materials. The primary outcome is body weight. Secondary outcomes include dietary fat, fruit, and vegetable intake; physical activity; stress, and affect. Mediators are self-efficacy, emotional coping response, social support, and autonomous motivation. Telephone interviews and in-person data collection at WIC offices occur at 3 time points: baseline, immediately, and 3 months after the 16-week intervention. Discussion: If MIM shows effectiveness, it could have a favorable impact on public health and community programs. The DVDs and PSGTs will be disseminated in WIC, Extension, clinical practice that promote healthy lifestyles for similar target audiences to make a broad contribution to the prevention of weight gain in low-income mothers. Also, our methodology can be adapted by researchers and community stakeholders to help other low-income populations prevent weight gain. Trial registration: Clinical Trials Number: NCT01839708.